The electrophoretic display (EPD) is a non-emissive device based on the electrophoresis phenomenon of charged pigment particles dispersed in a solvent. The display typically comprises two plates with electrodes placed opposing each other. One of the electrodes is usually transparent. An electrophoretic fluid composed of a colored solvent with charged pigment particles dispersed therein is enclosed between the two plates. When a voltage difference is imposed between the two electrodes, the pigment particles migrate to one side or the other causing either the color of the pigment particles or the color of the solvent being seen from the viewing side.
Alternatively, an electrophoretic fluid may comprise two types of charged pigment particles of contrasting colors and carrying opposite charges, and the two types of the charged pigment particles are dispersed in a clear solvent or solvent mixture. In this case, when a voltage difference is imposed between the two electrode plates, the two types of the charged pigment particles would move to opposite ends (top or bottom) in a display cell. Thus one of the colors of the two types of the charged pigment particles would be seen at the viewing side of the display cell.
For all types of electrophoretic display, the fluid contained within the individual display cells of the display is one of the most crucial parts of the device. The composition of the fluid determines, to a large extent, the performance of the device.